Electro-luminescent display device and method for fabricating the same

ABSTRACT

A top emission type electro-luminescent display device comprising a thin film transistor, an opaque electrode, an opaque layer, and an electro-luminescent medium layer. The thin film transistor overlies a substrate and is covered by an interlayer insulator. The opaque electrode and the opaque layer are successively disposed on the interlayer insulator, in which the opaque electrode is electrically connected to the thin film transistor and the opaque layer comprises an opening exposing a portion of the underlying opaque electrode. The electro-luminescent medium layer is disposed over the exposed portion of the opaque electrode. The transparent electrode is disposed on the opaque layer and conformally covers the surfaces of the opening and the electro-luminescent medium layer.

BACKGROUND

The invention relates to a flat panel display and in particular to a topemission type electro-luminescent (EL) device and method for fabricatingthe same.

Electro-luminescent (EL) devices, such as organic light-emitting diodes(OLEDs), are active lighting devices using organic materials. The ELdevice typically comprises an anode, a cathode, and an EL medium layerdisposed therebetween. When an electrical potential difference isapplied between the anode and the cathode, electrons and holes areinjected into the EL-medium layer from the cathode and the anode,respectively. The injected electrons and holes are then recombined,releasing energy as light.

FIG. 1 illustrates a conventional bottom emission typeelectro-luminescent device. As shown in FIG. 1, a buffer layer 102 isformed on a substrate 100. A thin film transistor 111 is disposed on thebuffer layer 102, comprising an active layer 104, a gate dielectriclayer 106, a gate electrode 107, and source and drain electrodes 109.The active layer 104, such as a polysilicon layer, is. disposed on thebuffer layer 102, comprising source and drain doping regions 105. Theactive layer 104 is covered by an insulating layer 106, such as asilicon nitride layer, serving as the gate dielectric layer. The gateelectrode 107 is disposed on the gate dielectric layer 106 overlying theactive layer 104 and covered by an interlayer dielectric (ILD) layer108. The source and drain electrodes 109 are respectively disposed onboth sides of the gate electrode 107 and electrically connected to thesource and drain doping regions 105, respectively, by the contact holesin the ILD layer 108 and the underlying insulating layer 106. A firstpassivation layer 110 covers the thin film transistor 111 and the ILDlayer 108, comprising a via hole to expose the source/drain electrode109. A transparent electrode 112, such as an indium tin oxide (ITO)layer, is formed on a portion of the first passivation layer 110 andelectrically connected to the exposed source/drain electrode 109 throughthe via hole. A second passivation layer is disposed on the firstpassivation layer 110 overlying the thin film transistor 111. An ELmedium layer 116 covers the second passivation layer 114 and thetransparent electrode 112. An opaque electrode 118, such as a metalmaterial, is formed on the EL medium layer 116.

In FIG. 1, the transparent and opaque electrodes 112 and 118 serve asthe anode and the cathode, respectively. Thus, the light is emitted in adownward direction from the EL medium layer 116 through the transparentelectrode 112, providing a bottom emission type EL display device. Thelight-emitting area of the bottom emission type EL display device,however, is limited by thin film transistors. For example, the apertureratio of the EL device is reduced while the number of the thin filmtransistors is increased. Accordingly, power consumption must beincreased to maintain the EL display panel brightness, reducing thelifetime of devices.

SUMMARY

An electro-luminescent display device and a method for fabricating thesame are provided. An embodiment of an electro-luminescent displaydevice comprises a substrate comprising a first region and a secondregion, a thin film transistor, an interlayer insulator, an opaqueelectrode, an opaque layer, an electro-luminescent medium layer, and atransparent electrode. The thin film transistor is disposed on the firstregion of the substrate. The interlayer insulator is disposed on thesecond region of the substrate and covers the thin film transistor. Theopaque electrode overlies the interlayer insulator and electricallyconnected to the thin film transistor. The opaque layer overlies theopaque electrode, having a first opening exposing a portion of theunderlying opaque electrode. The electro-luminescent medium layer isdisposed over the exposed portion of the opaque electrode. Thetransparent electrode is disposed on the opaque layer and conformallycovers the surfaces of first opening and the electro-luminescent mediumlayer.

An embodiment of a method comprises providing a substrate comprising afirst region and a second region. A thin film transistor is formed onthe first region of the substrate. An interlayer insulator is formed onthe second region of the substrate, covering the thin film transistor.An opaque electrode overlies the interlayer insulator, and electricallyconnects to the thin film transistor. An opaque layer overlies theopaque electrode, having a first opening exposing a portion of theunderlying opaque electrode. An electro-luminescent medium layer isformed over the exposed portion of the opaque electrode. A transparentelectrode is formed on the opaque layer and conformally covers thesurfaces of the first opening and the electro-luminescent medium layer.

DESCRIPTION OF THE DRAWINGS

An electro-luminescent display device and a method for forming the samewill become more fully understood from the detailed description givenhereinbelow and the accompanying drawings, given by way of illustrationonly and thus not intended to be limitative of the invention.

FIG. 1 is a cross-section of a conventional bottom emission typeelectro-luminescent display device.

FIGS. 2A to 2F are cross-sections of an embodiment of a method forforming an electro-luminescent display device.

DETAILED DESCRIPTION

An electro-luminescent display device and a method for forming the samewill be described in greater detail in the following. FIG. 2Fillustrates an embodiment of a top emission type electro-luminescentdisplay device. The device comprises a substrate 200 comprising a firstregion 10 and a second region 20, a thin film transistor 215, aninterlayer insulator 212, an opaque electrode 214, anelectro-luminescent medium layer 222, and a transparent electrode. 224.In some embodiments, the first region 10 may be a transistor region andthe second region 20 a light-emitting region. Moreover, the substrate200 is covered by a buffer layer 202. The thin film transistor 215 isdisposed on the buffer layer 202 of the first region 10 of the substrate200, comprising an active layer 204 comprising source and drain dopingregions 211, a gate dielectric layer 206, a gate electrode 207, andsource and drain electrodes 213. An interlayer dielectric (ILD) layer210 is disposed on the gate dielectric layer 206 and covers the gateelectrode 207.

The interlayer insulator 212 overlies the interlayer dielectric layer210 over the second region 20 of the substrate 200 and covers the thinfilm transistor 215 over the first region 10 of the substrate 200.Moreover, the interlayer insulator 212 comprises an opening to expose asource/drain electrode 213.

The opaque electrode 214 overlies the interlayer insulator 212 and iselectrically connected to the thin film transistor 215 through theexposed source/drain electrode 213. The opaque electrode 214 over thesecond region 20 of the substrate 200 has a relative height higher thanthat of thin film transistor 215 over the first region 10 of thesubstrate 200. A transparent conductive layer 216 may be optionallydisposed on the opaque electrode 214, serving as a portion of theelectrode 214, such that the work function of the electrode 214 canmatch the subsequent electro-luminescent medium layer 222.

An insulating layer (passivation layer) 218 and the opaque layer 220 aresuccessively disposed on the opaque electrode 214, in which theinsulating layer 218 comprises an opening 219 to expose a portion of theopaque electrode 214 having the transparent conductive layer 216 thereonand the opaque layer 220 an opening 221 above the opening 219. In someembodiments, the opening 221 is in the second region 20 of the substrate200 or across the first and second regions 10 and 20 of the substrate200. Here, only the former is depicted. Moreover, the opening 221 may belarger than the opening 219 to further increase the aperture ratio. Theelectro-luminescent medium layer 222 is disposed on the bottom of theopenings 221 and 219. The transparent electrode 224 is disposed on theopaque layer 220 and conformally covers the surfaces the opening 221 andthe electro-luminescent medium layer 222.

When an electrical potential difference is applied between theelectrodes 214 and 224, electrons and holes are injected into theelectro-luminescent medium layer 222 from the electrodes 214 and 224,respectively. The injected electrons and holes are then recombined,releasing energy as light. The light is reflected in an upward directionfrom the opaque electrode 214. Therefore, the light-emitting area(aperture ratio) is not reduced even if the number of the thin filmtransistors is increased, maintaining or increasing the brightness ofthe electro-luminescent display device. In other words, the powerconsumption is not increased, potentially extending the lifetime of theelectro-luminescent display device. Moreover, the opaque layer 220overlying the opaque electrode 214 may block light from lateralscattering by the electro-luminescent medium layer 222, therebyimproving wash-out effect, and consequently, display quality can beimproved.

FIGS. 2A to 2F are cross-sections of an embodiment of a method forfabricating a top emission type electro-luminescent display device. Asshown in FIG. 2A, a substrate 200, such as a glass or quartz substrate,comprising a plurality of transistor and light-emitting regions for theformation of thin film transistors and the electro-luminescent diodesthereon. Here, in order to simplify the diagram, only a first region 10and a second region 20 are depicted. For example, the first region 10may be a transistor region and the second region a light-emittingregion. A buffer layer 202 is formed on the substrate 200. In someembodiments, the buffer layer 202 may be a single layer or a stackstructure. For example, the buffer layer 202 can comprise a siliconnitride layer and an overlying silicon oxide layer. A semiconductorlayer (not shown) is subsequently formed on the buffer layer 202 andthen defined by conventional lithography and etching, to form apatterned semiconductor layer 204 over the first region 10 of thesubstrate 200, serving as the active layer of the thin film transistor.

As shown in FIG. 2B, an insulating layer 206, such as a silicon nitridelayer, is formed on the buffer layer 202 and covers the active layer204, serving as the gate dielectric layer of the thin film transistor.Thereafter, a metal layer (not shown) is formed on the insulating layer206 and then patterned by conventional lithography and etching to form apatterned metal layer 207 over the first region 10 of the substrate 200,serving as the gate electrode of the thin film transistor. Ionimplantation 209 is performed on the active layer 204 using the gateelectrode 207 as an implant mask to form source and drain doping regions211.

An interlayer dielectric layer 210 is deposited overlying the substrateshown in FIG. 2B. Contact holes are subsequently formed on both sides ofthe gate electrode 207 by etching the interlayer dielectric layer 210and the underlying insulating layer 206, exposing the source and draindoping regions 211, as shown in FIG. 3C.

As shown in FIG. 2D, a metal layer (not shown) is formed on theinterlayer dielectric layer 210 and fills the contact holes toelectrically connect the source and drain doping regions 211. The metallayer is then patterned by conventional lithography and etching to formsource and drain electrodes 213, thus the fabrication of a thin filmtransistor 215 is completed over the first region 10 of the substrate200. An interlayer insulator 212 is deposited on the interlayerdielectric layer 210 over the first and second regions 10 and 20 of thesubstrate 200 and covers the thin film transistor 215, serving as aplanarization layer. An opening 217 is formed in the interlayerinsulator 212 to expose a source/drain electrode 213.

As shown in FIG. 2E, an opaque conductive layer 214 is formed on theinterlayer insulator 212 and conformally covers the surface of theopening 217 to electrically connect the exposed source/drain electrode213. The opaque conductive layer serves as an electrode of anelectro-luminescent diode and a light reflective layer. Moreover, theopaque conductive layer 214 may be a single metal layer or multiplemetal layers. For example, the opaque conductive layer 214 may comprisealuminum, silver, aurum, titanium, nickel, chromium, copper, ferrum,manganese, platinum, zinc, or alloys thereof. In some embodiments, theopaque conductive layer 214 over the second region 20 of the substrate200 has a relative height exceeding that of the thin film transistor215, such that the subsequently formed electro-luminescent medium layercan also be relatively higher than the thin film transistor 215, therebyincreasing the aperture ratio. A transparent conductive layer 216, suchas an indium tin oxide (ITO) or indium zinc oxide (IZO) layer mayoptionally be deposited on the opaque electrode 214. The transparentconductive layer 216 serves as a portion of the electrode 214 of theelectro-luminescent diode, such that work function of the electrode 214matches the subsequently formed electro-luminescent medium layer. Notethat the-subsequently formed electro-luminescent medium layer must bedoped for work function match, as without forming the transparentconductive layer 216 between the electro-luminescent medium layer andthe electrode 214.

An insulating (passivation) layer 218 is formed overlying the opaqueelectrode 214 having a transparent conductive layer 216 thereon. Anopening 219 is subsequently formed in the insulating layer 218 in thesecond region 20 of the substrate 200.

As shown in FIG. 2F, an opaque layer 220 is formed on the insulatinglayer 218 (a critical step of this embodiment). As mentioned, the opaquelayer 220 blocks light from lateral scattering by the subsequentlyformed electro-luminescent medium layer, thereby improving wash outeffect. In some embodiments, the opaque layer 220 may comprise metal,metal oxide, organic material (for example, photoresist), or polymer.Preferably, the opaque layer 220 comprises metal, for example, aluminum,silver, aurum, titanium, nickel, chromium, copper, ferrum, manganese,platinum, zinc, or alloys thereof. Moreover, the opaque layer 220 may bea single layer or multiple layers, as the opaque electrode 214. As theopaque layer 220 is metal, lateral scattered light may be blocked in awave guide constituted by the opaque electrode 214 and the opaque layer220, thereby reducing light leakage. Another opening 221 is formed inthe opaque layer 220 over the opening 219, preferably larger than theopening 219, to block light emitted from the subsequently formedelectro-luminescent medium layer. In some embodiments, the opening 221can be formed across the first and the second regions 10 and 20 of thesubstrate 200. Thereafter, an electro-luminescent medium layer 222 isformed on the bottom of the openings 219 and 221, which may be a singlelayer or multiple layers. In some embodiments, the electro-luminescentmedium layer 222 may comprise a hole transport layer (HTL), an electrontransport layer (ETL), and an active or emissive layer sandwiched inbetween HTL and ETL. Here, in order to simplify the diagram, only asingle layer is depicted. A transparent electrode 224, such as ITO orIZO, is formed on the opaque layer 220 and conformally covers thesurfaces of the opening 221 and the electro-luminescent medium layer222, thus fabrication of an electro-luminescent diode 226 over thesecond region 20 of the substrate 200 is completed. Since the light isupward released from the electro-luminescent medium layer 222, theelectro-luminescent display device called the top emission type.

In some embodiments, the opaque layer 220 may be directly formed on theopaque electrode layer 214 without the insulating layer 218therebetween. Note that the opaque layer 220 may be an insulating layerin this case. For example, the opaque layer 220 may comprise metaloxide, organic material (such as photoresist), or polymer.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation to encompass all suchmodifications and similar arrangements.

1. An electro-luminescent display device, comprising: a substratecomprising a first region and a second region; a thin film transistordisposed on the first region of the substrate and comprising a pair ofsource/drain electrodes; an interlayer insulator disposed on the secondregion of the substrate and covering the thin film transistor; an opaqueelectrode overlying the interlayer insulator and electrically connectedto the thin film transistor, wherein one of the pair of source/drainelectrodes of the thin film transistor directly contacts the opaqueelectrode and the other is directly below the opaque electrode; anopaque layer, overlying the opaque electrode, having a first openingexposing a portion of the underlying opaque electrode, wherein theopaque electrode is extended across the entire bottom of the opaquelayer; an electro-luminescent medium layer disposed over the exposedportion of the opaque electrode and apart from the sidewall surface ofthe first opening and non-contacted with the sidewall surface of thefirst opening, wherein the top surface of the electro-luminescent mediumlayer is substantially below the top surface of the opaque layer; and atransparent electrode disposed on the opaque layer and directly on theexposed sidewall surface of the first opening and the top surface of theelectro-luminescent medium layer.
 2. The device as claimed in claim 1,wherein the opaque electrode over the second region of the substrate hasa relative position higher than that of the thin film transistor.
 3. Thedevice as claimed in claim 1, further comprising an indium tin oxidelayer disposed between the electro-luminescent medium layer and theopaque electrode.
 4. The device as claimed in claim 1, wherein theopaque electrode comprises metal.
 5. The device as claimed in claim 1,wherein the opaque layer comprises an organic material layer, a metaloxide layer, or a polymer layer.
 6. The device as claimed in claim 1,further comprising an insulating layer disposed between the opaqueelectrode and the opaque layer, having a second opening under the firstopening and exposing the opaque electrode.
 7. The device as claimed inclaim 6, wherein the opaque layer comprises a metal layer, an organicmaterial layer, a metal oxide layer, or a polymer layer.
 8. The deviceas claimed in claim 6, wherein the first opening is larger than thesecond opening.
 9. The device as claimed in claim 1, wherein the firstopening is in the second region of the substrate.
 10. The device asclaimed in claim 1, wherein the first opening is across the first andthe second regions of the substrate.
 11. A method for fabricating anelectro-luminescent display device, comprising: providing a substratecomprising a first region and a second region; forming a thin filmtransistor comprising a pair of source/drain electrodes on the firstregion of the substrate; forming an interlayer insulator on the secondregion of the substrate and covering the thin film transistor; formingan opaque electrode overlying the interlayer insulator and electricallyconnected to the thin film transistor, wherein one of the pair ofsource/drain electrodes of the thin film transistor directly contactsthe opaque electrode and the other is directly below opaque electrode;forming an opaque layer overlying the opaque electrode, having a firstopening exposing a portion of the underlying opaque electrode, whereinthe opaque electrode is extended across the entire bottom of the opaquelayer; forming an electro-luminescent medium layer over the exposedportion of the opaque electrode and apart from the sidewall surface ofthe first opening and non-contacted with the sidewall surface of thefirst opening, wherein the top surface of the electro-luminescent mediumlayer is substantially below the top surface of the opaque layer; andforming a transparent electrode on the opaque layer and directly on theexposed sidewall surfaces of the first opening and the top surface ofthe electro-luminescent medium layer.
 12. The method as claimed in claim11, wherein the opaque electrode over the second region of the substratehas a relative position higher than that of the thin film transistor.13. The method as claimed in claim 11, further forming an indium oxidelayer between the electro-luminescent medium layer and the opaqueelectrode.
 14. The method as claimed in claim 11, wherein the opaqueelectrode comprises a metal layer.
 15. The method as claimed in claim11, wherein the opaque layer comprises an organic material layer, ametal oxide layer, or a polymer layer.
 16. The method as claimed inclaim 11, further forming an insulating layer between the opaqueelectrode and the opaque layer, having a second opening under the firstopening and exposing the opaque electrode.
 17. The method as claimed inclaim 16, wherein the opaque layer comprises a metal layer, an organicmaterial layer, a metal oxide layer, or a polymer layer.
 18. The methodas claimed in claim 16, wherein the first opening is larger than thesecond opening.
 19. The device as claimed in claim 11, wherein the firstopening is in the second region of the substrate.
 20. The device asclaimed in claim 11, wherein the first opening is across the first andthe second regions of the substrate.